1. Field of the Invention
The present invention relates to an automatic selection apparatus of sheet material which detects defects of sheet material such as, for example, paper and selects good sheet material automatically and continuously.
2. Description of the Prior Art
Heretofore, selection of paper is generally made by human eyes. On the other hand, an automatic selection apparatus has been proposed as described above in which stacked sheets of paper are put on a belt one by one and carried so that a defect detection device disposed above the belt detects defects of the sheets of paper to distinguish whether the sheets of paper are good or bad. Furthermore, there has been proposed another apparatus in which the sheets of paper are carried while being held between upper and lower belts.
The conventional automatic selection apparatus carries the sheets of paper put on the belt or held between the upper and lower belts. Accordingly the carried sheets experience small vibrations in the carrying direction and in the transverse direction due to sliding generated between the belt and the sheets and between the belt and a driving portion of the belt. Consequently, it can not be distinguished whether a detected signal of the defect detection device is a signal due to small defect of the sheet of paper or a signal due to the vibration. Further, when a gap is provided in the carrying line of the sheets of paper in which the belt on which the sheets of paper are put or the belts between which the sheets of paper are held are disconnected, the carrying velocity of the sheet of paper is greatly reduced for a very short time when the leading edge of the sheet is transferred to a next belt after the leading edge has passed the gap and consequently the sheet of paper fluctuates. Accordingly, it is difficult for the detection device to detect a small defect of the sheet of paper. In this manner, the conventional automatic selection apparatus can not detect small defects accurately and has a defect detection capability greatly inferior to a defect by human eyes. Thus, the sheets of paper that are distinguished as good products by the apparatus are not used when they should be.